The general view of each of the i-TED modules as implemented in Geant4 is displayed in Fig. REF  (a). A critical parameter of this system is the distance between the two detection planes, so-called focal distance, which was set to 15 mm for all the simulations in this work. According to a previous work [1]}, this value ensures a good balance between efficiency an angular resolution. Each of the four i-TED modules was placed at a different distance (25, 50, 75 and 100 mm) from the sample to study its impact in the signal-to-background ratio (SBR).
